According to development of the information society, demands for display devices for displaying images are increasing in various forms, and demand for high-resolution display devices is also increasing. As a way for realizing a high-resolution display device, the number of pixels per unit area is increased, but the numbers of gate wirings and data wirings are increased in order to supply a gate signal and a data signal in accordance with increased pixels. However, as the number of gate wirings increases, a time (Gate on Time) for which a gate signal may be provided to one pixel is shortened, so that development of a thin film transistor with a high carrier mobility is required.
In addition, as a way for smooth moving picture playback, a way for increasing a driving frequency has been studied, and even when the driving frequency is increased, a time (Gate on Time) for which a gate signal may be provided to one pixel is shortened, so that development of a thin film transistor with a high carrier mobility is required.